Production of friction material



-NOV. 5, 1957 H, J, COFEK 2,811,750

PRODUCTION OF' FRICTION MATERIAL Filed Nov. "5,` 1954 2,811,750 PatentedNov. 5, 1957 United States ii arent PRODUCTION OF FRICTION MATERIALHenry J. Cofek, Stratford, Conn., assignor to Raybestos- Manhattan,Inc., Passaic, N. J., a corporation of New Jersey Application November5, 1954, Serial No. 467,054

3 Claims. (Cl. 18-55) This invention relates tothe production offriction material for use as brake linings, clutch facings, and thelike.

The present invention is particularly directed to improvements in themethod of producing friction material by compacting and shapingparticles of a preformed mixture to substantially final density andshape in continuous strip form by rolling.

For the foregoing process a mixture is made in a suitable device, suchas a dough mixer, of asbestos fibers, conventional friction modifyingagents and fillers, heathardenable organic binder material, and bindersolvent, the solvent being sufficient to permit good distribution of thebinder and the mix, but limited in amount so that the mix may be reducedto the form of relatively dry but somewhat tacky, granular, free-flowingparticles which can be fed by gravity from a hopper to the bite betweena pair of forming rollers, one of the rollers having a knurled orserrated periphery projecting into a AU-shaped periphery of another rollproviding a laterally confined opening between the rolls. A process andapparatus of such character is shown in the Novak and Cofek U. S. PatentNo. 2,620,320.

In order to provide granules of a character which can flow freely anduniformly by gravity, and in order to permit the formation of stripmaterial of uniform compactness and in the density and shapesubstantially that finally desired in a single pass through thedescribed rollers, it has heretofore been necessary that the asbestosfibers be of the very short fiber grades, and without long fibercontent, since the longer grades of fiber do not lend themselves touniform gravity feed because they tend to tangle and clump in thehopper, resulting in nonuniform compactness in the formed continuousstrip. On the other hand, it is desirable that the asbestos shouldcontain fibers ofthe longer grades, since the longer fibers providebetter reinforcement and hence impart greater strength to the nishedproduct. Heretofore the longer grades of asbestos fibers haveessentially been restricted to use in weaving processes, dry moldingtechniques, paper machines, sheeters orv die-casting techniques.

In accordance with the present invention is has been found that asbestosfibers of the longer grades may be employed in the mixture if the stripmaterial as first formed is passed at least once more between theforming rollers at which time a uniformly compacted strip results havingimproved strength in both the green and cured states. Further, productsof substantially equal strength may be formed with a smaller proportionof fibers of the longer grades as compared with the requirements whenusing the short fiber grades.

Although the strip material of the present invention does not requireother reinforcement, if desired a wire mesh or other reinforcement maybe incorporated on either the first forming pass or second compactingpass throughthe rollers.

The second pass of the strip material through the rollers. need not beof the preformed long-fiber-content Y strip alone, but lon this secondpass there may be formed another layer, by supplying additionalmaterial. from the supply hopper containingy the shorter grades offibrous asbestos without long fiber content. This second layer may be ofthe same or different thickness than the first, and may serve variousfunctions, such as reinforcing backing or a backing to provideacoustical proporties to overcome noise conditions in use..

As a further alternative, when forming multi-ply material, the initiallyformed long-fiber-containing strip may comprise the reinforcing backingfor the composite. As another alternative, multi-ply strip material maybe formed of two layers of long asbestos fiber content which mayotherwise vary as to proportons and character of constituents. In suchcase, after the second layer is deposited in the second run, a third runis made through the rollers, without added material, to evenly compactthe second layer.

The second pass may also be employed to imbed a wire mesh or otherreinforcement between the two layers of material 'so as to position thereinforcement closer to the neutral axis of the strip and to minimizeproblems of machining and warpage in cure and use which otherwise occurwhen wire mesh is merely imbedded in the surface of thestrip, as isprovided by a single pass, and as more fully described and claimed in mycopending ap,- plication Serial No. 467,055, ledof even date herewith.

As indicated previously, the present invention is characterized by the`employment of fibrous asbestos having a content of long grade fibers,and it will be understood that as commercially provided in the standarddesignated grades in accordance with Canadian Chrysotile AsbestosClassification, a `grade of asbestos will have fibers of differentlengths and that even the highest spinning grades will contain some veryshort material or fines passing a 10-mesh screen, but will still beclassified as long fiber, and therefore, Vas employed in the followingspecification and claims, it will be understood that the term asbestosof long liber content is intended to include the grades of groups 3, 4and 5 of the aforesaid classification where the majority of the fibersare retained on a lO-mesh screen having a screen opening of 0.053 inch,and mixtures of said grades. Group 3 contains iibers retained ona-/z-inch screen opening, and group 4 contains fibers retained on a4mesh screen. ln group 5, a majority of the fibers are retained on theIO-mesh screen and only a minor amount pass said screen. Asdistinguished from this, asbestos of groups 6 and 7 are characterized bya content of fibrous material, the majority of which passes a 10-meshscreen, and minor amounts are retained on the 10-mesh screen, and arethus designated as short asbestos fibers. y

The accompanying drawings diagrammatically illustrate the process of theinvention a-nd the apparatus employed for forming the products thereof.

Fig. l of the drawings is a diagrammatic sectional elevation of arolling apparatus employed in the production of friction materials ofthe class to which they present invention is directed.

Fig. 2 is a fragmentary front elevation of the rolling apparatus.

Fig. 3 is a section on the line 3:*3 of Fig. 1.

Fig. 4 is a diagrammatic illustration similar tothat of Fig. lillustrating a modified process step.

Fig. 5 is a section on the line 5 5 of Fig. 4.

In the production of strip material from an asbestosbinder compositionwherein they asbestos is characterized by a long fiber content ashereinbefore defined, a mix is prepared wherein the solids are composedof from about 25% to about 75% by weight of asbestos lof lonlg fibercontent; from about 15% to about 30% by weight ofheat hard'ena'bleorganic binder material; and fromvabout 0 to about 60% conventionalfriction material fillers, which term is inclusive of accelerators,lubricants, and relatively inert organic and inorganic frictionaugmenting and modifying agents, all well known in the friction-materialart.

The asbestos may be composed of any of the grades of long fiber contentor mixtures thereof, as previously described. The heat-hardenableorganic binders may be bodied or unbodied drying oils, such as bodiedsynthetic or natural drying oil, as for example China-wood oil orlinseed oil bodied by blowing and/or heat; thermosetting resins such asphenol-aldehyde resins, preferably aqueous, partial-condensationphenol-formaldehyde resin solutions, such as those described in CofekPatent 2,586,150; natural or synthetic rubbers such as styrene oracrylonitrile copolymers with butadiene, polychloroprene, and the like;or mixtures of the aforesaid binders, together with vulcanizing orhardening agents for the aforesaid rubber materials.

A typical example of the solids content of a suitable mixture for thepractice of the present invention is 40% by weight of asbestos of longfiber content composed of a mixture of 4T and 3R grades; 17% by weightof heathardenable organic binder; 18% by weight of metal chips; and 25%by weight of other inert fillers, accelerators, lubricants, and frictionaugmenting agents. These materials are mixed in a dough mixer togetherwith solvent for the binder adequate to dissolve and distribute thebinder over the remaining solids in the mix, the solvent being justsufficient to permit good distribution but limited in amount so that themix may be reduced to the form of relatively dry granular particleswhich can subsequently be fed by gravity from a hopper to the bite ofthe forming rolls subsequently to be described, and compacted and shapedthereby to a dense composition which will have a minimum shrinkage.

The solvent for the oil and rubber binders may be the conventionalhydrocarbon solvents, and when employing aqueous solutions ofphenol-formaldehyde resin as previously indicated, the aqueous phase ofthe resin solution provides the binder solvent. The mixing is continueduntil the mix has a comminuted texture and is in the form of loosepellets or nodules. These are permitted to age at room temperature forabout one or two days and then pulverized in a hammer mill to produceparticles,

which are generally termed granules of irregular shape, L'

roughly 1,46" to 1A in diameter. These particles are highly compressble,and although they are normally dry, they have strong tack on beingpressed together. Further, although these granules can be and areemployed in the process herein described, by reason of the long asbestosliber content, there is a tendency for these particles to tangle andclump in the hopper, with the result that they do not ow in a uniformmanner, but rather as nonuniform granule aggregates.

Thus referring to the drawing, for the purpose of compacting andshaping, the described granular particle material is placed in thehopper 11 wherein it is agitated by means of the spike agitators 12 andowed therefrom by gravity through the hopper opening 13 into thereservoir 14 and passed therefrom by means of the adjustable feed gate15, to and between the nip of the rolls 16 and 17. Roll 16 has a knurledsurface and is suitably mounted for rotation on the shaft 18. Roll 17suitably mounted for rotation on the shaft 19 is provided with a pair ofanges or confining walls 20, the roll 16 being spaced from the roll 17and projecting within the anges or confining walls of the latter. Inoperation, the feed gate is adjusted to a spacing from the periphery ofthe roll 17 somewhat greater than the desired thickness of the issuingstrip material 21.

However, as previously indicated, this strip material 21, as a result ofinherent nonuniformity and uneven flow of feed stock is initially ofnonuniform compactness. In order to overcome this, the strip `21 is thenpassed a second time between the rolls 16 and 17 without any addedstock; or, in the alternative, it is passed in a continuous operationbetween a successive pair of rolls 16 and 17', which is similar to therolls 16 and 17, to thereupon result in a strip 22 of substantiallyuniform compactuess and cross-sectional dimension substantiallyconforming to that of the ultimately desired friction material, such asbrake lining, with a density of from about to about of theoretical uponevaporation of the solvent content and binder cure. This strip has highstrength and is self-sustaining in both the green and the cured state,and does not require any wire or open mesh reinforcement, although suchreinforcement may be provided if desired. Although not illustrated, itwill be understood that not only may this strip material be produced ina width suitable for brake linings, but also in wider widths suitablefor the production of clutch facings; the latter, however, requiringadded blanking.

The issuing strip material 22 may be rolled up on a mandrel into coilsof desired length, dried free of solvent, and then subjected to heat tocure and harden the binder content. The material may thereafter befinished in a suitable manner, as by grinding to remove roughness. Itmay be alternatively cut into single brake segment lengths, and theselengths cured to segments having xed curvature.

Alternatively, a multi-ply product may be formed as illustrated in Fig.4. In this case the preformed strip 21 is passed through a rollingapparatus as previously described, by passing the strip over the guideroll 23 and around roll 16 so that it is caused to pass a second timebetween the pair of rolls 16 and 17 to thereby reduce it to a conditionof substantially uniform compactness. In this instance there issimultaneously supplied from the hopper 11 granules of anasbestos-containing composition wherein the asbestos is all of shortfiber content and the granules are of a free-flowing nature. Thiscomposition 24 may be of an asbestos heat-hardenable organic binderfriction material composition, such as that described in the two patentshereinbefore mentioned, having an asbestos content from about 50% toabout 75% by weight of all short fiber when this second layer is to forma friction face.

On the other hand, the composition 24 applied as the second layer neednot comprise the friction face but rather may act as a backing. Thus,for example7 a typical reinforcing back composition is composed of 19%by weight of short bers of 7D grade; 16% by weight of heat-hardenableorganic binder material; 28% by weight of metal chips; and 37% by weightof other fillers, accelerators, lubricants, friction augmenting andmodifying agents. ln the alternative, the composition 24 may provide abacking of acoustical properties to overcome a noise condition of anotherwise satisfactory brake lining, and for this purpose the asbestosfibers may be replaced in part with, for example, about 50% ofcomminuted or granular cork particles of from about l0 to about 40 meshsize.

It will thus be understood that although the composition of the granularparticle material 24 may have frictional properties adapted for use asthe operative friction surface, so as to form a composite stripgenerally indicated as 2S composed of the layers 26 and 27, with thelayer 27 being the reinforcing layer resulting from the rerolling of thepreformed strip 21 in Fig. 4, these may be reversed so that the strip21, rerolled as strip 27, may be of greater thickness and form thefriction surface, and the layer 26 resulting from the mix 24 may berelatively thinner and provide a backing which may be of reinforcingcharacter or have acoustical properties as described. In any event, thepreformed strip 21, by having passed the second time between the rollers16 and 17, has as a result been reduced to a composition of desireduniform compactness and high strength.

Although not illustrated, it will be understood that the composition 24may be characterized by a content of asbestos of long fibers, such as incomposition 10, although the proportions of components between the twosuccessive applied layers, and the nature of the fillers, when employed,may be different. 1n such event, however, it is necessary to again passthis dual-ply composite strip a third time through the pair of rolls16-17 or 16-17' so that the last applied layer of long asbestos bercontent will have passed between the compacting rollers at least twicewhereby the last applied layer may be reduced to a condition ofsubstantially uniform compactness.

It will also be understood, as more particularly described and claimedin my aforementioned copending application filed of even date herewith,that a strip of reinforcing wire or other open-mesh fabric may beimbedded between the plies of the hereinbefore described multi-ply stripmaterial, by passing same, for example, over the strip 21 in Fig. 2 sothat it becomes imbedded between the ultimate layers 26 and 27.

It will thus be seen that in accordance with the hereinbefore describedinvention I have been able to form friction materials with asbestos oflong fiber content by means of the rolling process wherein the use ofsuch asbestos was heretofore thought unfeasible, with the result thatfriction material of novel properties and strength characteristic oflong asbestos fibers is now obtainable in this economical procedure foruse either as friction material per se or as reinforcing backing forfriction material. It will be further evident that I have been able toproduce friction material of unitary character composed of a pluralityof blended layers wherein each layer may be of different character andperform a different function, one of the layers being characterized byasbestos of long fiber content with the attendant advantages of suchasbestos material.

I claim:

1. The method of making friction material which comprises, rollinggranular friction composition particle material comprised of a mixtureof asbestos of long fiber content wherein a majority of the bers areretained on a -rnesh screen having a screen opening of .053 inch, heathardenable organic binder material and binder solvent, between spacedoppositely rotating surfaces while laterally confining the material, tocompact and shape the particles into the form of a dense continuousstrip, subjecting said strip, prior to cure of its binder, to asuccessive like rolling to reduce it to a condition of substantiallyuniform compactness and simultaneously adding granular compositionparticle material comprised of a mixture of asbestos of all short fibercontent wherein a majority of the fibers pass said screen, heathardenable organic binder material and binder solvent, to form a4consolidated multiply strip.

2. The method of making friction material which com- Y prises, rollinggranular friction composition particle material comprised of a mixtureof asbestos of long fiber content, heat-hardenable organic bindermaterial and binder solvent, between spaced oppositely rotating surfaceswhile laterally conning the material, to compact and shape the particlesinto the form of a dense continuous strip, subjecting said strip, priorto cure of its binder content, to a successive like rolling to reduce itto a condition of substantially uniform compactness and simultaneouslyadding granular composition particle material comprised of a mixture ofasbestos of all short ber content, comminuted cork particles,heat-hardenable organic binder material and binder solvent, to form aconsolidated multi-ply strip having a backing of acoustical property.

3. T he method of making friction material which comprises, rollinggranular friction composition particle material comprised of a mixtureof asbestos of long ber content, heat-hardenable organic binder materialand binder solvent, between spaced oppositely rotating surfaces whilelaterally confining the material, to compact and shape the particlesinto the form of a dense continuous strip, subjecting said strip, priorto cure of its binder content, to a successive like rolling whilesimultaneously adding similar granular composition particle material oflong asbestos ber content to form a consolidated multi-ply strip, andsubjecting the latter strip, prior to cure of its binder content, to asuccessive like rolling, in the absence of added material of longasbestos fiber content, to reduce it to a condition of substantiallyuniform compactness.

References Cited in the le of this patent -UNITED STATES PATENTS2,070,600 Jenett Feb. 16, 1937 2,185,333 Denman Jan. 2, 1940 2,309,571Bruce et al Ian. 26, 1943 2,428,771 Almy Oct. 14, 1947 2,534,607 Laheret al. Dec. 19, 1950 2,539,631 Kuzmick Jan. 30, 1951 2,554,128 SpokesMay 22, 1951 2,620,320 Novak et a1 Dec. 2, 1952 FOREIGN PATENTS 464,176Great Britain Apr. 13, 1937

1. THE METHOD OF MAKING FRICTION MATERIAL WHICH COMPRISES, ROLLINGGRANULA FRICTION COMROSITION PARTICL MATERIAL COMPRISED OF A MIXTURE OFASBESTOS OF LONG FIBER CONTENT WHEREIN A MAJORITY OF THE FIBERS ARERETAINED ON A 10-MESH SCREEN HAVING A SCREEN OPENING OF .053 INCH, HEATHARDENABLE ORGANIC BINDER MATERIAL AND BINDER SOLVENT, BETWEEN SPACEDOPPOSITELY ROTATING SURFACES WHILE LATERALLY CONFINING THE MATERIAL, TOCOMPACT AND SHAPE THE PARTICLES INTO THE FORM OF A DENSE CONTINUOUSSTRIP, SUB-